OBJECTIVES: (1) To search for viruses which may play an etiological role in the syndrome of acute infectious nonbacterial gastroenteritis of infants, children, and adults; (2) to cultivate (in vitro) the viral agent(s) of acute infectious nonbacterial gastroenteritis; (3) to study the biophysical, immunological, and epidemiological characteristics of such agent(s); (4) to reproduce the syndrome experimentally in volunteers for the purpose of a) studying the pathophysiological and immunological responses of the host, and b) assaying the infectivity of such viral agents; (5) to develop effective immunoprophylaxis for the viruses of acute, infectious, non-bacterial gastroenteritis.